The present invention concerns a digital signal processing circuit which finds an application in the European digital cellular radio system defined by the Groupe Speciale Mobile (hereinafter called the "GSM") of the European Telecommunications Standards Institute (ETSI).
The circuit is designed to carry out in particular the digital part of the signal processing needed in a mobile, portable or hand-portable terminal. In this context, "terminal" means the equipment providing access to the communication network. This application is not the only one as the circuit might be used in other elements of the cellular radio system.
The signal processing circuit must therefore provide all the functions described below, these functions being specified in the form of GSM recommendations. Given the number and the complexity of these functions the circuit must necessarily have a programmable structure. The solution commonly employed is to implement this circuit with a parallel architecture, that is to say to use multiple processors each of which carries out some of these functions, which solution is described in particular in the articles "Advanced VLSI components for digital cellular mobile radio"--Electrical Communication, volume 63, No 4, pages 409 through 414 by Ranier et al. and "Signal processing requirements in Pan-european digital mobile communications"--IEEE International symposium on circuits and systems, volume 2, 7 through 9 June 1988, pages 1803 through 1810. This solution offers some flexibility as the various functions are distributed. However, it requires interface units between the processors and a control unit to coordinate the operation of the processors. These units make a significant contribution to the overall size of the circuit. What is more, as the processors employed are relatively complex it is difficult to envisage the integration of the circuit into a single component using currently available technologies. As the circuit comprises multiple components it is bulky and this is an obstacle to miniaturization of the terminal into which it is incorporated. The circuit is also costly. Furthermore the software of the circuit includes, in addition to the various programs needed for executing its specific functions, programs which enable the units and processors of the circuit to cooperate. It is therefore large.
Another solution would be to employ a single processor for the circuit providing all the signal processing functions. A processor of this kind would have to be very powerful in terms of the number of instructions it could execute per unit time and could not be manufactured using currently available technologies.
In any event, even though the high speed of progress in microelectronics makes the availability of a processor of this type feasible in the shorter or longer term, it would be very costly. Also, the signal processing software would be complex because it would have to be of the multitasking type and a large amount of memory would be needed to store it.